Re: [sfc] WGLC for https://datatracker.ietf.org/doc/draft-ietf-sfc-ioam-nsh/

[Greg Mirsky <[e-mail]>]

Hi Shwetha,
thank you for the detailed response to my comments. Please feel free to
share any updates you're considering for the next version. I'll be glad to
work together on these.
I have several follow-up notes in-lined below under the GIM>> tag.

Regards,
Greg

On Tue, Oct 26, 2021 at 6:51 PM Shwetha Bhandari <
[e-mail]> wrote:

> Hi Greg,
>
> Sorry for the very late reply. Please find responses to your comments
> inline @Shwetha:
>
>
>
> On Wed, Sep 8, 2021 at 3:30 AM Greg Mirsky <[e-mail]> wrote:
>
>> Dear Authors and All,
>> I've read the current version of the draft and have some comments I'd
>> like to share with you. I much appreciate your thoughts on where this work
>> should go considering developments in other IETF WGs. Please find my notes
>> and questions below:
>>
>>    - It is stated in the Abstract that:
>>
>>    In-situ Operations, Administration, and Maintenance (IOAM) records
>>    operational and telemetry information in the packet while the packet
>>    traverses a path between two points in the network.
>>
>> But that is the case only for the pre-allocated and incremental trace
>> option types. The Direct Export option
>> <https://urldefense.com/v3/__https://datatracker.ietf.org/doc/draft-ietf-ippm-ioam-direct-export/__;!!MZ3Fw45to5uY!db6q3n8-5YqHkLtf3wyeBoUpO72v7UzeDtfPNhyePahNAYMo9eFdQxxBWM4C7Z0OJKE0jphubQ$>
>> does not write telemetry data into the data packet itself but export
>> telemetry information in a specially constructed packet.
>> And as we are talking about different IOAM trace options, the question of
>> the scope of this document seems appropriate. There is a WGLC on two
>> IOAM documents
>> <https://urldefense.com/v3/__https://mailarchive.ietf.org/arch/msg/ippm/A0OcGQ5LlNjnjfRVp_iUTMYMrcs/__;!!MZ3Fw45to5uY!db6q3n8-5YqHkLtf3wyeBoUpO72v7UzeDtfPNhyePahNAYMo9eFdQxxBWM4C7Z0OJKHOndSFRg$>
>> active through September 15th at the IPPM WG. I believe that it would be
>> beneficial if we had a single document that describes the applicability of
>> IOAM in all its functionality defined by documents in IPPM WG. Of course,
>> that cannot be a moving target as that would not be helpful. But since the
>> IPPM WG discusses the progress of two IOAM documents, it could be a great
>> time to address the applicability of the Direct Export trace type
>> <https://urldefense.com/v3/__https://datatracker.ietf.org/doc/draft-ietf-ippm-ioam-direct-export/__;!!MZ3Fw45to5uY!db6q3n8-5YqHkLtf3wyeBoUpO72v7UzeDtfPNhyePahNAYMo9eFdQxxBWM4C7Z0OJKE0jphubQ$>
>> and Loopback and Active flags defined in draft-ietf-ippm-ioam-flags
>> <https://urldefense.com/v3/__https://datatracker.ietf.org/doc/draft-ietf-ippm-ioam-flags/__;!!MZ3Fw45to5uY!db6q3n8-5YqHkLtf3wyeBoUpO72v7UzeDtfPNhyePahNAYMo9eFdQxxBWM4C7Z0OJKHO7lReVw$>.
>> It would be concerning to have more than one SFC document describing the
>> applicability of the generic IOAM mechanisms
>>
>>
> Shwetha> This is a fair point. We will revise the  draft with text in the
> abstract and Section 3 IOAM-Type to be updated to include the usage of
> trace and DEX options.  The encapsulation of IOAM options within NSH itself
> in its current form already supports all the IOAM Option Type defined both
> from draft-ietf-ippm-ioam-data and draft-ietf-ippm-ioam-direct-export
> along with the flags supported within the options. Hence the
> IOAM-data-field definitions in the draft will remain unchanged.
>
GIM>> I agree that the definitions of the IOAM data-fields are invariant in
various data plane encapsulations. You likely follow the discussion of the
IAOM Direct Export and IOAM flags on the IPPM WG list. I think that for SFC
NSH, IOAM Direct Export could be as simple as "use the local policy". The
applicability of the Loopback and Active flags seems to require detailed
explanation by SFP actors.

>
>
>>
>>
>>    - The location of the IOAM header in the SFC NSH-encapsulated packet
>>    is defined in Section 3:
>>
>>    IOAM-Data-Fields are carried in NSH
>>    using a next protocol header which follows the NSH MD context
>>    headers.
>>
>> I've checked RFC 8300 but couldn't find it defines the Next Protocol
>> header. Also, it appears that NSH Context headers are optional. Hence my
>> question. Is the presence of an NSH Context header required when using
>> IOAM? Could you clarify which mechanism is used to identify the payload of
>> an SFC NSH-encapsulated packet as IOAM?
>>
>> Shwetha> We will reword it, it is not Next Protocol header but using IOAM
> as a Next Protocol as described in Section 4.1 and requested in IANA
> section. Following is the proposed text to align with the RFC 8300
> reference to context headers following base header and service path header:
> "The NSH is defined in [RFC8300].  IOAM-Data-Fields are carried in
> NSH using a next protocol to identify IOAM data fields that follows NSH
> context headers."
>
GIM>> I think that RFC 8300 views data following Context Headers as NSH
payload, not being "in NSH".

>
>>    - If I understand the format of the IOAM header defined in Section 3
>>    correctly, the header's length is limited by 1020 octets, while the
>>    effective length containing IOAM options and data - 1016 octets. Is that
>>    correct? What is the recommended technique of collecting IOAM data that
>>    exceeds that limit?
>>
>> Shwetha > IOAM options inherently support specifying the size limits at
> the node that added the IOAM options. While operationalizing the solution
> the data types included and number of nodes expected to be adding the data
> should be selected. This is covered in deployment
> considerations draft-brockners-opsawg-ioam-deployment.
>
>>
>>    - In Section 4.1, I've found the text reflecting the history of the
>>    discussion about how to carry the IOAM header using NSH encapsulation. As
>>    the text has no normative value, I suggest moving it into an Appendix.
>>
>> Shwetha > Agreed, revised draft will have this section moved to Appendix.
>
GIM>> Thank you.

>
>>    - I find the rules of handling the O-bit in NSH listed in Section 4.2
>>    inconsistent and confusing. The IOAM header is not part of NSH
>>    encapsulation but is a part of the payload. But in one case, when user data
>>    follows it, the O-bit must not be set as. If there's no user data after the
>>    IOAM header, then the O-bit must be set. But from the perspective of NSH
>>    encapsulation, it includes specially constructed data added for the sole
>>    purpose of collecting OAM/telemetry information. Then, why, in one case,
>>    the O-bit is cleared and in the other set if, in both cases, the
>>    NSH-encapsulated packet is used to perform the OAM function?
>>
>> Shwetha > The reason for not setting the O-bit for packets that contains
> actual user data is because RFC 8300 has " SF/SFF/SFC Proxy/Classifier
> implementations that do not support
>
>       SFC OAM procedures SHOULD discard packets with O bit set". It will be undesirable to discard packets with O-bit set that carry user data as IOAM can be inserted insitu.
>
> For synthetic traffic created for OAM along with IOAM-data-fields in NSH following the NSH OAM function with 0-bit set is desirable.
>
>  GIM>> This is an interesting situation. I agree that there could be an
SFC element not supporting "SFC OAM procedures" (not clear what these are).
By the same token, would such SFC element support IOAM, be capable of
processing IOAM without adverse impact to user data? I am not certain and
it seems that it might be better to recommend that NSH packets with IOAM be
dropped by an SFP element if it does not support "SFC OAM". What are your
thoughts?


>
> Thanks,
> Shwetha
>
>> I much appreciate your consideration of my comments and questions and
>> looking forward to your feedback.
>>
>> Regards,
>> Greg
>>
>> On Wed, Aug 18, 2021 at 5:32 AM James Guichard <
>> [e-mail]> wrote:
>>
>>> Dear WG:
>>>
>>>
>>>
>>> This email starts a 2 week Working Group Last Call for
>>> draft-ietf-sfc-ioam-nsh [1].
>>>
>>>
>>>
>>> Please read this document if you haven’t read the most recent version
>>> and send your comments to the SFC WG list no later than September 1st
>>> 2021.
>>>
>>>
>>>
>>> If you are raising a point which you expect will be specifically debated
>>> on the mailing list, consider using a specific email/thread for this point.
>>>
>>>
>>>
>>> Lastly, if you are an author or contributor please response to indicate
>>> whether you know of any undisclosed IPR related to this document.
>>>
>>>
>>>
>>> Thanks!
>>>
>>>
>>>
>>> Jim & Joel
>>>
>>>
>>>
>>> [1] https://datatracker.ietf.org/doc/draft-ietf-sfc-ioam-nsh/
>>> <https://urldefense.com/v3/__https://datatracker.ietf.org/doc/draft-ietf-sfc-ioam-nsh/__;!!MZ3Fw45to5uY!db6q3n8-5YqHkLtf3wyeBoUpO72v7UzeDtfPNhyePahNAYMo9eFdQxxBWM4C7Z0OJKHdTiRE6A$>
>>>
>>>
>>>
>>>
>>>
>>>
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>>